1. Field of the invention
The present invention relates to an armature core for use in a motor and, in more particular, to a magnetic treating means for treating magnetic flux in an open slot formed between mutually adjoining salient poles provided in the armature core.
2. Related art
As shown in FIG. 10, a conventional armature core 110 comprises a plurality of, for example, three salient poles 116 which are respectively disposed at uniform intervals from each other and are projected radially from the central portion 118 of the armature core 110, while each of the salient poles 116 includes an arm portion 112 and an umbrella portion 114. And, between the mutually adjoining umbrella portions 114 of the salient poles 116, there is formed an open slot 120 which extends in the peripheral direction of the armature core 110 to provide a space necessary for a winding operation to wind a coil 122 around the arm portion 112 of the salient pole 116.
Referring to the coil winding operation, as shown in FIG. 10, while guiding a lead wire 124, the armature core 110 is rotated (in the direction of an arrow A shown in FIG. 10) around a nozzle 126 from which the lead wire 124 is played out, so that the lead wire 124 is wound around the arm portion 112 of the armature core 110. The open slot 120 forms an operation space in order to prevent the umbrella portion 114 from interfering with the winding operation, while the nozzle 126 which is moved in a controlled manner forms the coil 122. The coil 122 can be wound by the nozzle 126 around the arm portion 112 but only in the range that is shown by reference character .delta.. Part of the inside portion of the umbrella portion 114 is filled up with the winding collapsed portion of the coil 122 that is produced in the end portion thereof, but the remaining portions thereof are left as a dead space 128.
On the other hand, the distance of the opening 130 of the open slots 120 formed between the mutually adjoining umbrella portions 114 causes a change in the magnetic resistance due to the angle of rotation of the motor, which in turn provides a factor in a cogging due to Maxwell stress which is in proportion to the square of a magnetic flux density, thereby obstructing the smooth continuous rotation of the motor.
That is, in order to facilitate the winding operation of the coil, if the gap of the opening 130 of the open slot 120 is widened too much, then the magnetism of the present portion decreases, so that the magnetic resistance increases to thereby increase the cogging. On the other hand, if the width or gap of the opening 130 is narrowed, then the winding operation of the coil 120 becomes difficult, which not only lowers the productivity of the coil 120 but also reduces the occupation rate of the volume of the coil 120 to thereby make it impossible to obtain a required motor output.
In order to solve the above problems, in Unexamined Japanese Utility Model Publication Hei. 6-88178, an additional core is provided in the adjoining space (open slot) formed between the salient poles after completion of the coil winding operation. However, according to this proposal, because the structure of the armature core is complicated to a certain degree, the cost thereof is caused to increase. Also, there is a possibility that a magnetic path can short-circuit between the mutually adjoining umbrella portions to thereby deteriorate the efficiency of the motor.